This invention relates to a method and an apparatus of optical modulation using superconductive oxide material, and particularly to a method and apparatus of optical modulation useful for various optical recording heads, optical shutters and optical switches which perform light path switching or light intensity modulation.
The invention also relates to a method of detecting an external physical state such as the current, magnetic field, temperature, pressure, etc. by utilization of superconductive material, and particularly to a method of detecting an external physical state useful for various sensors and readers operating in binary (0 or 1) mode.
Optical switches and optical modulators are described, for example, in publication "Optronics", 1987, No. 4, pp. 70-75. As prior art of optical shutters, the shutter using liquid-crystal is known, as described in pp. 97-103 of the above publication. A variety of materials for optical sensors have been proposed, as described, for example, in publication "Optronics", 1983, No. 7, pp. 36-43. These publications, however, give no suggestion of using superconductive material for the optical modulation method or device.
Recently, the optical communication system using optical fiber has been put into practice by being supported by the advanced development of the optical system made up primarily of the light source, optical path and optical receiver. In addition to the above fundamental system components, there is an intense demand of developing optical switches and modulation devices for realizing a higher grade optical system.
The optical switch is used for switching in the event of failure in the optical transmission path or optical reception device, and also will be used for optical switching. Optical switches fall into categories including: (1) mechanical system, (2) optoelectric system, (3) opto-acoustic system, (4) optomagnetic system, (5) opto-thermal system, and (6) molecular orientation system.
A conceivable optical switch includes several ports formed in a PLZT waveguide layer and operates to switch the light path by utilization of a change in refractive index of PLZT in response to voltage application, as described for example in the Technical Study Report of The Institute of Electronics and Communication Engineers of Japan, OQE 84-16, pp. 57-, 1984.
Various optical modulation devices of a traveling wave type using a LiNbO.sub.3 waveguide have been studied, as described, for example, in the publication of The Institute of Electronics and Communication Engineers of Japan, Vol. 69 (1986), pp. 141-.
The above-mentioned prior art optical devices utilize a change in refractive index of the material based on the opto-electric phenomena. The refractive index change is as small as 1% or less and therefore it is merely applicable to light path switching for the light propagated in the waveguide.